This invention relates to novel burner manifold apparatuses. More particularly, this invention relates to burner manifold apparatuses for micromachined burners, such as micromachined silicon burners.
It is known to form various articles, such as crucibles, tubing, lenses, and optical waveguides, by reacting a precursor in the flame of a burner to produce a soot and then depositing the soot on a receptor surface. This process is particularly useful for the formation of optical waveguide preforms made from doped and undoped silica soot, including planar waveguides and waveguide fibers.
The waveguide formation process generally involves reacting a silicon-containing precursor in a burner flame generated by a combustible gas, such as a mixture of methane and oxygen, and depositing the silica soot on an appropriately shaped receptor surface. In this process, silicon-containing materials typically are vaporized at a location remote from the burner. The vaporized raw materials are transported to the burner by a carrier gas. There, they are volatilized and hydrolyzed to produce soot particles. The soot particles then collect on the receptor surface. The receptor surface may be a flat substrate in the case of planar waveguide fabrication, a rotating starting rod (bait tube) in the case of vapor axial deposition (VAD) for waveguide fiber fabrication, or a rotating mandrel in the case of outside vapor deposition (OVD) for waveguide fiber fabrication.
Numerous burner designs have been developed for use in vapor delivery precursor processes, and at least one liquid delivery precursor process has been contemplated, as disclosed in co-pending application Ser. No. 08/767,653 to Hawtof et al, incorporated herein by reference. Whether the precursor is delivered to the burner in vapor form or liquid form, it is important that the burner receives a distributed, even stream of precursor. This consideration is particularly important during waveguide manufacture to form accurate refractive index profiles.
In the recent past, burners for deposition of metal oxide soot have been proposed having orifices and supply channels on a small scale. The channels and orifices in these burners may have widths or diameters less than 150 microns, for example, as disclosed in commonly-owned provisional application Ser. No. 60/068,255 entitled xe2x80x9cBurner and Method For Producing Metal Oxide Soot,xe2x80x9d incorporated herein by reference.
As a result, there has arisen a need for a burner manifold that may be used in conjunction with these micromachined burners and may distribute fluid uniformly and evenly to the burners. In conventional large-scale burners, this uniformity was achieved by equally large concentric rings. This solution, however, is not practical for use with micromachined burners.
With the advent of micromachined burners, it is desirable to have a burner manifold apparatus that evenly and uniformly distributes fluid (either vapor or liquid) to the micromachined burners.
A burner manifold apparatus in accordance with the present invention comprises fluid inlets, fluid outlets, and a plurality of fluid passages. The fluid passages extend between the fluid inlets and the fluid outlets to deliver reactants to the combustion site of a chemical vapor deposition process. The fluid passages converge toward each other from the fluid inlets to the fluid outlets in that inlets of the fluid passages are spaced farther apart than outlets of the fluid passages. This arrangement facilitates delivery of reactant precursor fluid from a macro scale delivery system to a micro scale burner. The fluid passages preferably have a smaller cross-sectional area at their outlet than at their inlet.
The fluid passages generally are isolated from one another so that some fluid passages transport reactant precursor materials and other fluid passages transport combustion materials. The fluid passages at the fluid outlets are preferably shaped to match the geometry of the burner. In a preferred embodiment, the fluid outlets are slot shaped or formed as a series of in-line round holes.
The burner manifold apparatus further includes at least one pressure inducing restriction device for passing fluid therethrough in evenly distributed, narrow elongated streams. The pressure inducing restriction device is positioned between the fluid inlets and the fluid outlets. The pressure inducing restriction device preferably comprises a plate having a series of slots or linearly arrayed apertures for emitting fluid therefrom in generally linear streams of droplets.
One embodiment of the present invention includes a manifold base having a top, a bottom, a front wall, a back wall, and two side walls. The manifold base defines horizontal passages therethrough that extend between the side walls, vertical passages extending from a position within the manifold base to the top of the manifold base, and fluid inlet ports. Each fluid inlet port is located on either the front wall or the back wall of the manifold base, and each is in fluid communication with at least one of the horizontal and vertical passages. The horizontal passages preferably are parallel to the top and the bottom of the manifold base, and the vertical passages preferably are parallel-to the side walls of the manifold base.
The burner manifold apparatus of the first embodiment also includes a plate mounted to the top of the manifold base. The plate defines a plurality of apertures therethrough. At least one aperture is positioned at a location above an exit of each of the vertical passages of the manifold base to allow passage of fluid from the vertical passages through the plate.
The vertical passages of the manifold base are symmetric about a first axis bisecting the top of the manifold base. The vertical passages preferably include a central vertical passage and pairs of vertical passages, each pair defined by two vertical passages spaced equidistant from the first axis. Each pair intersects a particular horizontal passage to create an array of passages within the manifold to distribute fluid symmetrically about the first axis.
The apparatus of the first embodiment further includes a manifold burner mount mounted to the top of the plate. The manifold burner mount defines fluid passages that extend from a bottom of the manifold burner mount to a top of the manifold burner mount. These fluid passages are arranged to converge such that a distance between adjacent fluid passages is greater at the inlet of the manifold burner mount than at the outlet of the manifold burner mount.
The burner manifold apparatus further comprises a first gasket positioned between the manifold base and the plate. The first gasket has slots therein in alignment with grooves in the top of the manifold base. A second gasket preferably is positioned between the plate and the manifold burner mount. This second gasket has slots in alignment with the slots in the first gasket. A burner gasket may be placed upon the manifold burner mount. The burner gasket has slots in alignment with the exits of the fluid passages in the manifold burner mount.
Securing elements, such as clamps, may be mounted to the top of the manifold burner mount for releasably securing a burner to the manifold burner mount. The clamps each have an outer edge and an inner edge, and the inner edge has a shoulder that engages the burner. Further, the inner edge of each clamp has a tapered surface that tapers away from the top of the manifold burner mount.
A second embodiment of the subject burner manifold apparatus includes a plurality of manifold elements positioned in a stacked arrangement on top of a base element. The manifold elements fluidly communicate with each other via fluid passages therein. Each of the manifold elements has a different number of fluid passages, preferably increasing by two for each successive element located higher on the stack. These fluid passages converge toward each other at the outlet of the manifold apparatus. Each of the manifold elements has at least one fluid inlet port, and preferably two, with the exception of the lowermost manifold element.
The fluid passages preferably are linear and extend vertically through the manifold elements. The outermost fluid passages of each of the manifold elements communicate with a fluid inlet port, and inner fluid passages are isolated from the outermost fluid passages to isolate the fluids introduced into different manifold elements. The fluid passages of adjacent manifold elements are in vertical alignment. Like the fluid passages in the burner mount of the first embodiment, the fluid passages of this second embodiment are symmetric about a central fluid passage.
Gaskets are disposed between adjacent ones of the manifold elements. The gaskets have slots therethrough to allow passage of fluid. The gaskets preferably are formed from an elastomer material.
In a third embodiment of the invention, the burner manifold comprises a tapered section having a first end and a second end, where the first end has a larger surface area than the second end. The fluid inlets are located at the first end of the manifold, and the fluid outlets are located at the second end of the manifold. The tapered section preferably has a truncated cone shape.
The burner manifold may also comprises a top section coextensive with the tapered section. The top section has a first end adjoining the second end of the tapered section, and a second end for carrying a burner.
The tapered section and the top section of this third embodiment define a plurality of fluid passages therethrough to convey fluid from the first end of the tapered section to the second end of the top section. In a preferred embodiment, the fluid passages run generally parallel to each other and converge toward each other from the fluid inlets at the first end of the tapered section to the fluid outlets at the second end of the top section. Selected ones of the fluid passages may be blocked or plugged to select, by elimination, which passages provide fluid flow.
In this third embodiment, the burner manifold is formed by an extrusion process. The burner manifold tapers from a first end to a second end or, alternatively, has a tapered section located between the first end and the second end. This can be done, for example, by plastically transforming a preform of parallel channels (honeycomb substrate) into a funnel of funneling channels. Two suitable transforming processes are hot draw down and reduction extrusion. xe2x80x9cHot draw downxe2x80x9d is a viscous forming process carried out on viscously sintered preforms and is described in commonly-owned U.S. patent application Ser. No. 09/299,766 entitled xe2x80x9cRedrawn Capillary Imaging Reservoirxe2x80x9d, the specification of which is hereby incorporated herein by reference. xe2x80x9cReduction extrusionxe2x80x9d is a plastic forming process carried out on unsintered particulate preforms as illustrated in Corning""s U.S. Pat. No. 6,299,958 entitled xe2x80x9cManufacture of Cellular Honeycomb Structuresxe2x80x9d, the specification of which is hereby incorporated herein by reference. Particulates of metal, plastic, ceramic and/or glass are compounded and extruded to make the preform. The top section of the manifold may be cylindrical, rectangular, or any other shape suitable for carrying a burner.
A fourth embodiment of the invention includes a plurality of burner mounts, a plurality of plates, and a single manifold base. The manifold has a thickness dimension between the front wall and the back wall that is greater than a thickness dimension of the burner mounts and the plates such that a plurality of burner mount/plate combinations may be mounted to the manifold.
The burner manifold apparatus of the present invention achieves a number of advantages over conventional burner manifolds. For example, the burner manifold apparatus bridges the gap between the conventional xe2x80x9cmacroxe2x80x9d world of manifolds and the xe2x80x9cmicroxe2x80x9d world of micromachined silicon wafer burners.
Another advantage is that the burner manifold apparatus is capable of use in conjunction with a burner having a linear flame array that evenly distributes fluid through the manifold and to either side of the burner""s linear flame array.
Still another advantage is that the burner manifold apparatus may securely and precisely mount a micromachined burner wafer in place.
A further advantage is that the burner manifold apparatus may be arranged adjacent other assemblies to form an array of adjacent burners, which generate closely adjacent burner flames.
Yet a further advantage is that the burner manifold apparatus may be produced by an extrusion process or, alternatively, a hot draw down process.
Still a further advantage of the burner manifold apparatus is that the burner may be mounted to the burner mount by an anodic bond, without the need for clamps or other mechanical attachment means.
The manifold of the present invention also enables and facilitates the use of miniature micromachined burners in applications for depositing silica soot, in particular for making high purity soot for optical waveguide manufacturing processes.
Additional advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.